This invention relates, in general, to semiconductor devices, and more particularly, to sensors and methods of fabrication.
Semiconductor devices such as piezoresistive pressure sensors can utilize a thin semiconductor layer, or sensor diaphragm, as a sensing or active element. A piezoresistor is formed in the sensor diaphragm, and the resistance of the piezoresistor varies with the deformation of the sensor diaphragm. One method for forming such a structure first forms cavities in a first substrate using an anisotropic etch with potassium hydroxide (KOH). The cavity is then covered with a second substrate which acts as a diaphragm. Preferably, the second substrate should be bonded to the first substrate under a vacuum condition so that the cavity is sealed and can act as a reference pressure.
Unfortunately, the current state of the art of manufacturing equipment cannot provide a system which is capable of bonding large quantities of wafers under vacuum conditions. Currently, only single wafer bonding equipment is available for production facilities. This equipment tends to have poor throughput, which consequently increases manufacturing cost of the sensors produced. Accordingly, it would be very advantageous to provide a method for forming sensor structures that could use existing semiconductor processing equipment, but at an improved throughput compared to traditional wafer bonding equipment.